C3 and rheumatic disorder: In one study of 304 SLE patients, 285 patients with other rheumatic diseases, and 205 healthy individuals, the AUC for the presence of SLE was 0.79 ± 0.02 with antibodies to double-stranded DNA, 0.73 ± 0.02 with complement C3, and 0.72 ± 0.02 with complement C4 [61].